• The Journal of the Acoustical Society of Korea
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• v.7 no.2
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• pp.51-64
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• 1988

The frequency synthesizer thar has very short transient time is the key to construct the Fast Frequency Hopping(FFH) system. A Direct Digital Frequency Synthesizer(DDFS) whose transient time is in the nS range has been implemented and the performance of which has been examined through this paper. And by considering the hopping characteristic it is confirmed that the DDFS is suitable for the FFH system. Finally an improvement method which can greatly enhances the SNR with the state-of-the-art techniques and simplifies the system design is presented.

• Electronics and Telecommunications Trends
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• v.16 no.6 s.72
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• pp.92-100
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• 2001

본 논문에서는 국내 기술기준에서 정하고 있는 주파수 호핑 스펙트럼 확산(FHSS) 방식을 사용하는 무선기기에 대한 전파의 질 측정항목과 그에 따른 구체적인 전도성 측정절차에 관하여 서술하였다. 본문에서는 측정에 관련된 일반적인 사항으로부터 주파수 허용편차, 점유주파수대역폭, 공중선전력, 불요발사, 호핑 주파수의 체류시간, 중첩성 및 호핑의 개수 등의 항목들에 대한 세부적인 측정절차와 함께 예시로써 블루투스(bluetooth) 기기를 이용한 실제 측정결과를 함께 제시하고 있다.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2018.06a
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• pp.264-266
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• 2018

본 논문에서는 빔-호핑 위성 전송 시스템을 운용하기 위해 필수적으로 이루어져야 하는 빔 스위칭 타임 플랜 (Beam Switching Time Plan, BSTP) 동기 기법을 제안한다. 제안하는 기법은 게이트웨이의 변조 모듈에서 SF (super-frame) 신호를 전송한 후, 레퍼런스 수신 모듈에서 신호 전송 후 프레임 검출이 일어나기까지 걸리는 시간과 유효한 신호 검출 후 프레임 검출이 일어나기까지 걸리는 시간을 이용하여 BSTP 동기를 이룬다.

• Journal of KIISE:Information Networking
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• v.36 no.5
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• pp.383-388
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• 2009

In this paper, we focus on the retransmission following transmission failure in impulse radio ultra wideband (IR-UWB). The reasons of transmission failure are classified and a new 'selfish' retransmission protocol is proposed because time hopping can support multiple transmissions at the same time. Selfish retransmission protocol retransmits packets immediately without any kind of timeout or channel observation. Simulation results show that the proposed protocol improves throughput up to 50% and decreases retransmission delay also up to 70%, compared to a conventional retransmission system in IR-UWB.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.2
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• pp.402-407
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• 2005

The PLL synthesizer is used in communication system until now because it have several merits, such as broad bandwidth, high accuracy and stability of frequency But it is difficult to use in the third generation mobile communication systems that need frequency hopping at a high speed because of its long frequency hopping time. In this paper, we designed the frequency synthesizer that generate frequencies randomly at a high speed using the DDS technology.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2012.07a
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• pp.195-198
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• 2012

MB-OFDM UWB시스템은 TFC(Time-Frequency Code)를 이용하여 시간/주파수 호핑을 수행한다. 이를 통해 주파수 영역에서 다이버시티 효과를 갖는 동시에 사용되는 다른 piconet간의 간섭을 최소할 수 있다. 송신단에서는 프리앰블을 전송할 때부터 해당 TFC에 맞게 호핑을 하면서 전송을 하기 때문에 수신단에서는 신호의 시작을 추정하는 패킷 검출은 매우 중요한 과제이다. 따라서 본 논문에서는 MB-OFDM UWB시스템을 위한 간단하고 효율적인 패킷 검출 방법을 제안하였다. 시뮬레이션 수행 결과 제안된 방법은 기존 방법보다 약 0.5 dB의 SNR 개선 결과가 있는 것으로 밝혀졌다.

• Journal of Advanced Navigation Technology
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• v.5 no.1
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• pp.11-18
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• 2001

In this paper, we evaluated the performance of Orthogonal MC/FH-CDMA system considering the hit of frequency hopping patterns, and obtained the degree of the performance improvement by adopting TCM scheme under frequency selective Rayleigh fading channel. From the performance analysis, it is known that the error performance is improved, since delay time relative to symbol time is reduced as the number of carrier is increased. On the other hand, it is found that BER performance is improved about $5{\times}10^{-2}$ degree by adopting TCM scheme, and higher S/N is required if the QoS of voice (BER = $10^{-3}$) must be achieved.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.11 no.2
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• pp.102-110
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• 2012

ZigBee networks developed for low power and short range communication are being used as home network solution for ubiquitous computing. However, as smart phones and tablet PCs have been widely used, WLANs which use same frequency with ZigBee networks have been increasingly used. Therefore, radio frequency interference causes many problems. To solve radio frequency interference problem among ZigBee networks and WLANs, many researches focus on designing interference minimization schemes in ZigBee networks. However, existing schemes have problems that have waste of resource for detecting interference, and have unnecessary time to avoid interference. In this paper, we propose an interference minimization scheme to solve radio frequency interference in ZigBee networks. The proposed scheme detects interference using ACK mechanism to reduce waste of resource, and avoids interference using table driven channel hopping scheme which is faster than existed schemes. The performance of proposed interference minimization scheme is evaluated by using OPNET simulator. Through the simulation result, we prove that proposed scheme has faster channel hopping than existing schemes.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.17 no.1
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• pp.38-46
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• 1992

In this thesis, a high speed code synchronization circuit is implemented, which is applicable to frequency hopping FSK tranceiver within 68-88 MIBz band- width. synchronization Process consists of two steps, initial synchronization and tracking. A modified matched filter method using two channel passive correlators matched with short hopping frequencies, synchronization prcfix. is proposed for initial synchronization. To increase probability of initial synchronization, prefix are transmitted repeatedly. The outputs of correlators are sent to synchronization decision circuit, and code start time Is extracted by synchronizatlon decision circuit-Modified matched fitter method makes it possible to reduce complexity in hardware and obtain code acquisition rapidly.Clock recovery circuit regenerates PN code clock for tracking.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.1A
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• pp.1-11
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• 2009

In OFDMA or SC-FDMA systems one can generate time varying channels or frequency selective channels using multiple transmit antennas to achieve diversity without special space-time processing at the receivers. While low channel coding rate needs to be used for distributed-allocation SC-FDMA systems with a phase rolling technique to produce time fluctuation, relatively high channel coding rate can be used when cyclic delay diversity is used to increase frequency selectivity assuming quasi-static channel. On the other hand, for block-hopping SC-FDMA systems there is no significant difference between two diversity techniques in terms of optimal channel coding rates.